GB2329137A

GB2329137A - Vacuum coating apparatus

Info

Publication number: GB2329137A
Application number: GB9810838A
Authority: GB
Inventors: Derek William Whittle
Original assignee: UNIVERSAL FINISHING SYSTEMS CO
Current assignee: UNIVERSAL FINISHING SYSTEMS CO
Priority date: 1997-09-13
Filing date: 1998-05-21
Publication date: 1999-03-17
Anticipated expiration: 2018-05-21
Also published as: GB9810838D0; GB2329137B

Abstract

A vacuum coating apparatus, comprises: an application stage 1 for applying a surface coating to a product, comprising a chamber 11 having inlet and outlet ports for passing a product through the chamber, means 19 located within said chamber for applying coating to the product, and means for subjecting said chamber to a partial vacuum sufficient to inhibit leakage of the coating from the chamber; and a recovery stage 2 located downstream of said application stage for recovering excess coating from said product, said recovery stage comprising a recovery chamber 12 having inlet and outlet ports for permitting passage of a product through the recovery chamber, said inlet and outlet ports being configured to closely correspond to the cross section of the product, means for subjecting said recovery chamber to a vacuum sufficient to draw air into said recovery chamber through said inlet and outlet ports such that air flow over the product in the region of the inlet and outlet ports removes excess coating, and means for collecting excess coating from said recovery chamber.

Description

VACUUM COATING APPARATUS The present invention relates to the field of vacuum coating apparatus used to apply a surface coating to, for example, elongate wood components for the joinery industry.

A known vacuum coating apparatus I described in Applicant's own earlier Application GB 2145442 A, wherein an elongate product is passed through a closed application chamber via close fitting inlet and outlet ports, the chamber being evacuated by a vacuum pump such that coating to be applied to the product is drawn up into the application chamber by the vacuum and coats the section of the product in the chamber. Excess coating is drawn over a weir and is returned by gravity to a re.servoir. The evacuation of the chamber further draws air at high speed past the product at the inlet and outlet ports due to the relatively small gap around the product. This air flow contains the treatment fluid in the chamber, and removes excess fluid from the surface of the product.

It has been found that, despite the 1SP of baffles and filters between the chamber and the vacuum pump, certain types of product will, over time, and in particular when the apparatus is subject to continuous use, migrate along the vacuum system and contaminate the vacuum pump.

The introduction of further baffles and filters inevitably reduces the overall efficiency and performance of the vacuum arrangement. It is therefore an aim c the present invention to provide a vacuum coating apparatus which minimises coating contamination of the vacuum system.

According to the present invention there is provided a vacuum coating apparatus, comprising: an application stage for applying a surface coating to a product, comprising a chamber having inlet and outlet ports for passing a product through the chamber, means located within said chamber for the applying coating to the product, and means for subjecting said chamber to a partial vacuum sufficient to inhibit leakage of the coating from the chamber; and a recovery stage, located downstream of said application stage, said recovery stage for recovering excess coating from said product, said recovery stage comprising a recovery chamber having inlet and outlet ports for passing a product through the recovery chamber, said inlet and outlet ports being configured to closely correspond to a cross section of the product, means for subjecting said recovery chamber to a vacuum sufficient to draw air into said recovery chamber through said inlet and outlet ports such that air flow over the product in the region of the inlet and outlet ports removes excess coating, and means for collecting excess coating from said recovery chamber.

The application stage is preferably formed by a spray chamber housing a spray head for spraying the product with a coating, allowing the product to be coated around part or all of its surface as desired.

Preferably a spray head in the form of a ring or torroid is provided and has inwardly directed radial fluid ducts which may receive nozzles and/or blanking-off inserts. The partial vacuum created in the application chamber is preferably relatively light, of the order of 50 millibars, sufficient to prevent leakage of the coating from the chamber. The excess coating in the application chamber is preferably drawn by the vacuum through a series of baffles and filters and returned to a reservoir. The relatively light vacuum used for the application chamber significantly reduces migration of the coating toward the vacuum pump.

The recovery stage preferably uses inter-changeable templates at the inlet and outlet ports configured to match the product being coated, ideally leaving a gap of the order of 2 or 3 millimetres evenly around the product. A high pressure vacuum of the order of 300 to 400 millibar is used in the recovery stage to ensure relatively high speed airflow through the inlet and outlet ports. Controlling the strength of the vacuum controls the speed of the air flow, which in turn determines the amount of coating removed from the product by the recovery stage. For example, the product might leave the application stage with a coating averaging 40 micrometers in thickness, which may be reduced to the order of 5 micrometers in the recovery stage. However, since only relatively small amounts of coating are present in the recovery stage, contamination of the vacuum system is again minimised. The baffles and filters employed in the vacuum arrangement of the recovery stage can be selected so as to remove the relatively small amounts of coating, whilst minimising the negative effects on the performance and efficiency of the vacuum.

Preferably the application chamber and recovery chamber or the support frame thereof are mounted on a support base via resilient means so as to enable the chambers to respond to deflectional movements of a workpiece to thereby achieve an even or approximately even peripheral spacing around the workpiece and the surrounding part of the inlet/outlet parts. There are three guide rollers (not shown) at the entrance and exit to the application and recovery chamber combination for an elongate workpiece and mounted on the same support frame thereas. Separately and mounted on the floor there are feed and removal means for the workpiece. The elongate workpiece can move in position between the feed and guide means to cause the spacing between the inlet and outlet apertures or parts in the chambers to be undesirably irregular and such can be overcome in a preferred embodiment of the invention, by mounting the two chambers (and the guide wheels therefor) on shock absorbing means such as air springs or other resilient or shock absorbing and anti-vibration means which accommodate for tube deflections.

Thus advantages are obtained by mounting the application chamber and the recovery chamber on shock absorbing and anti-vibration means - units such as mechanical springs or other shock absorbing means but preferably air springs which are preferably pressure adjustable rubber shock absorbing means. This ensures an even as possible spacing between the edges of the entry aperture and the workpiece to be coated which is particularly important when elongate workpieces such as tubes are being fed in.

Further advantages and preferred features of the present invention will be apparent from the following description of a preferred embodiment with reference to the accompanying drawings, in which: Fig. 1 is a forward elevation of the apparatus; Fig. 2 is a plan view of the apparatus; Fig. 3 is a sectional side view of the application stage; Fig. 4 is a sectional side view of the recovery stage; Fig. 5 is a schematic section through an alternative construction of coating application means or spray ring; Fig. 6 is a section on the line C-C of Fig. 5; and Fig. 7 is a side elevation of an application chamber (behind which is an aligned recovery chamber (not shown)) and illustrating air spring mounting of the support frame therefor.

Referring to Figs. 1 and 2, the vacuum coating apparatus described herein may be used for a wide variety of products and coatings. Particular, non exclusive, examples include paints, stains, preservatives and other treatments. A particular example, familiar to persons skilled in the art, is a 100% solid acrylic UV curable surface coating, used to provide a durable, protective and aesthetically pleasing surface coating. The coating apparatus is suitable for use with a wide variety of products, including wood products such as moulding, curtain poles, tool handles, and snooker cues, of a variety of materials including wood, plastics material and metal.

Another particular example is the application of a corrosion inhibiting protective surface coating to rolled steel tube at the end of its manufacturing process.

The product is supplied to the coating apparatus by transport means (not shcwn) such as a conveyor belt or roller feed system, with the product preferably oriented longitudinally toward th2 apparatus and in a horizontal plane.

Referring to Figs. 1 and 2, the preferred apparatus comprises two separate stages, namely an application stage 1 having a spray head operating under low pressure vacuum, and a recovery stage 2 operating under high pressure vacuum.

Referring to Figs. 1 and 3, the product to be coated is fed to the apptication stage 1 (in the direction of arrow 3 shown in Fig. 1) and into a box-like application chamber 11. The application chamber 11 is shown in more detail in Fig. 3 with its side cover removed to reveal a spray ring 19 with apertures and arranged, in this embodiment, as a square spray ring having spray apertures along its inwardly facing surface. The spray ring 19 is conveniently provided with elbows at each corner for easy disassembly for cleaning, and for clearing product jams. Coating is supplied to the spray ring 19 by a fluid pump arrangement (not shown) from a reservoir 31. The product passes through corresponding and aligned inlet ard outlet ports in opposite walls of the chamber, of which only outlet port 17 can be seen in Fig. 3. The outlet poit 17 is partially covered in use by a template having arl aperture closely corresponding to the cross section of the product. The majority of the excess coating sprayed frow.

spray ring 19 onto the product falls by gravity to the bottom of the application chamber 11 and is returned via a return pipe 15 to the reservoir 31 for re-use.

It is desired to contain the coating within the application stage, in order to prevent contamination of the surrounding area, and to provide a clean working environment for operators of the apparatus. For this purpose. a vacuum arrangement is employed to draw air ite the application chamber 11 through inlet and outlet ports 17 past the product being coated. Air is drawn from th application chamber 11 via a coupling pipe 13 into a baffle tower 33 having a plurality of baffle plates 35 which collect urXused coating from the drawn air, as will be familiar to the skilled person. One or more filters 37 are provided at the top of the baffle tower 33 to further clean the air drawn off via an outlet 39 to a vacuum pump or turbine arrangement (not shown) . Typically, the vacuum pump operates at a vacuum of around 50 to 60 millibars.

Air flow in the application chamber 11 further has he advantage of creating turbulence to ensure an even coating around the product.

In the embodiment shown, the product passes through an air gap, ideally above a drip tray (not shown) into a box-like recovery chamber 12 of the recovery stage 2.

Referring to Fig. 4, the recovery chamber 12 is of generally smaller dimensions than the application chamber 11, for efficient air flow. Air is drawn at high speed through inlet and outlet ports 18 in opposite side walls of the recovery chamber 12 past the coated product. As shown in Fig. 4, the inlet and outlet ports of the recovery chamber 12 are relatively large as siown by area 20, and are partially covered by a template 18 closely corresponding to the cross-section of the product. The air flow past the product draws off the surface coating, to leave a coating of the desired thickness. Air drawn through the application chamber 12 exits via a coupling pipe 14 into a baffle tower 34 of similar construction to the baffle tower 33 of the application stage 1 and proceeds via a filter 38 to an exit port 40 coupled to a high pressure vacuum arrangement (not shown) operating in the region of 300 to 400 millibars, i.e. at a ratio of about 6:1 to 8:1 with respect to the application stage 1. The relatively small amounts of coating present in the air flow from the recovery chamber 12 are collected in the baffle tower 34 and returned to a second reservoir 32. Coating also falls by gravity to the bottom of the recovery chamber 12 and is returned via pipe 16 to reservoir 32.

The air flow in the application and recovery chambers 11 and 12 may be simply and conveniently controlled using a by-pass valve 41, 42 shown in Fig. 1 for introducing air into baffle towers 33 and 34. The valves 41,42 may simply comprise inlet apertures and a control flap for each with a manual or remote control operating a feedback system. The chambers 11 ard 12 are optionally supported by shear-off bolts, in order that the chambers 11, 12 may readily shear from their supports, such as during a product jam, without damaging the remainder of the apparatus.

The apparatus advantageously applies and recovers the coating in one pass, with the product then subsequently being transported to further stages, such as an ultraviolet light stage used to cure the coating.

It has been found that for some products such as steel tube, water and other contaminants from earlier stages in the manufacturing process are present within the tube, and is drawn therefrom by the high pressure vacuum as the product passes through the recovery stage. The use of a separate second reservoir 32 allows the recovered coating to be checked for the presence of contaminants, such as water, before optionally being returned to the first reservoir 31 for re-use.

In Fig. 3 the spray ring 19 is simply a bent tube closed at one end having apertures therein to permit fluid to be sprayed onto the workpiece/product to be coated but the resultant application is irregular and does not permit flexibility of adjustment of the spraying effect and in some instances the fluid from an aperture may not contact the workpiece. In Figs. 5 and 6 an improved spray ring 43 is illustrated within application chamber 11' having an air and fluid/vapour extraction duct or pipe 13 and a fluid return pipe 15'. Fluid i5 supplied via duct 44 to detachable ring 43.

Spray ring 43 is formed from two main parts namely a channelled fluid ducting part 45 and a cover plate 46 securable thereto to cover the ducts. Ducting part 45 is an annular/torroidal member having a fluid inlet duct 47 connectable to duct 44 for receiving fluid. Duct 47 runs into annular/torroidal channel 48 from which there extends a plurality of radial channels 49 directed to a workpiece 50 in the form of a cylilrdrical tube 50. The ends of radial channels 49 may have nozzles (not shown) detachably located therein or be optionally closed off if required.

Thus an even and adjustable spray arrangement is possible.

In Fig. 7 the application chamber 11" and recovery chamber (not shown but located behind chamber 11" and aligned therewith) are mounted on a rigid support framework 50 which in turn is mounted on a support frame 51 via four air springs 52 of known type whose pressure and thus acticn are adjustable. The mounting of the chambers via aIr springs r2 or other resilient means providing a shock absorbing and anti-vibration function, enables the chambers and, in particular, the workpiece receiving ports to adjust in position in response to deviations of an elongate workpiece to maintain an even as possible spacing around the wokpiece at the inlet and outlet ports of each chamber.

It is also envisaged to provide a heated supply tank (not shown) for the coating fluid which improves the flowability thereof and thus provides easier application and improved results. Suitable heating means for the coating fluid and control therefore will be provided.

Also according to a preferred embodiment of the invention, a motorised pressure adjustment is provided (nowt shown) either for remote control or for automatic control dependent on a vacuum pressure sensor and adjusts the vacuum in the chambers by displacement of a control valve such as a flap of an inlet aperture e.g. teardrop flap.

Suitable feedback systems may be provided or a remote control or a manual adjustment control means.

The apparatus described herein advantageous' significantly inhibits migration of the coating into +e vacuum pumping systems, because a low pressure vacuum used at the application stage where large amounts of coating are present, and a high pressure vacuum is used at the recovery stage where only small amounts of coating are present. The apparatus avoids the need for frequent preventative maintenance and cleaning of the baffles 35, 36 and the filters 37, 38, thereby reducing the down time when the apparatus is out of use. The apparatus may be used continuously for long periods, advantageously for coating a -ontinuously produced product such as rolled steel tube.

Claims

1. A vacuum coating apparatus, comprising: an application stage for applying a surface coating to a product, comprising a chamber having inlet and outlet ports for passing a product through the chamber, means located within said chamber for applying coating to the product, and means for subjecting said chamber to a partial vacuum sufficient to inhibit leakage of the coating from the chamber; and a recovery stage located downstream of said application stage for recovering excess coating from said product, said recovery stage comprising a recovery chamber having inlet and outlet ports for permitting passage of a product through the recovery chamber, said inlet and outlet ports being configured to closely correspond to the cross section of the product, means for subjecting said recovery chamber to a vacuum sufficient to draw air into said recovery chamber through said inlet and outlet ports such that air flow over the product in the region of the inlet and outlet ports removes excess coating, and means for collecting excess coating from said recovery chamber.

2. Apparatus as claimed in claim 1, in which the application stage is formed by a spray chamber housing a spray head for spraying the product with a coating, allowing the product to be coated around part or all of its surface as desired.

3. Apparatus as claimed in claim 1 or 2, in which the partial vacuum created in the application chamber is relatively light, of the order of 50 millibars, sufficient to prevent leakage of the coating from the chamber.

4. Apparatus as claimed in any of claims 1 to 3, in which the excess coating in the application chamber is drawn by the vacuum through a series of baffles and filters and returned to a reservoir.

5. Apparatus as claimed in at least claim 3, in which the relatively light vacuum used for the application chamber is such as to significantly reduce migration of the coating toward the vacuum pump.

6. Apparatus as claimed in any of claims 1 to 5, in which the recovery stage includes inter-changeable templates at the inlet and outlet ports configured to match the product being coated.

7. Apparatus as claimed in claim 6, in which the templates are such as to leave a gap of the order of 2 or 3 millimetres evenly around the product.

8. Apparatus as claimed in any of claims 1 to 7, in which a high pressure vacuum of the order of 300 to 400 millibar is used in the recovery stage to ensure relatively high speed airflow through the inlet and outlet ports.

9. Apparatus as claimed in at least claim 4, in which the baffles and filters employed in the vacuum arrangement of the recovery stage are selected so as to remove the relatively small amounts of coating, whilst minimising the negative effects on the performance and efficiency of the vacuum.

10. Apparatus as claimed in any of claims 1 to 9, in which the means for applying the coating comprises: an annular spray head having a plurality of radially inwardly directed spray ducts.

11. Apparatus as claimed in any of claims 1 to 10, in which the application chamber and recovery chamber are mounted on resilient means so as to accommodate any deflections of a workpiece.

12. Apparatus as claimed in any of claims 1 to 11, in which heating means are provided associated with a reservoir or supply tank for the coating fluid.

13. Apparatus as claimed in any of claims 1 to 12, in which the vacuum extraction pressure is controlled by a motorised valve controlled remotely and manually or automatically by a feedback system.

14. Vacuum coating apparatus substantially as herein described with reference to the accompanying drawings.